Hi, new poster here, I wanted to get feedback and advice on my situation. Basically, I installed a new 4870 on two motherboards and both are now completely disabled. I've never had an upgrade go so bad. Here are the details: First system was a Asus Maximus Formula, Q6600, Corsair HX620 PSU, 2x2Gb of Corsair TWIN2X4096-6400C5 memory, evga stock 8800GT, Vista 64-bit. No overclocking or BIOS mods of the CPU, memory or 8800GT. The system has been working since Jan 2008 and been pretty flawless. I uninstalled the 8800GT and Nvidia drivers, put in the 4870, connected the two 6-pin connectors and turned on the system. The fan on the 4870 spins up but sputters, slows down, then spins up again, over and over. It never achieves a steady rotation. The system never posts or boots at all. Turn off the power, turn on again. Same result. Removed the 4870, reinstalled the 8800GT and turn on the system. System powers up for a second, then shuts down. A second later, powers up again, then shuts down. It's caught in this endless loop. No post or BIOS at all. I reset CMOS, tried both the 4870 and 8800GT in the other PCI-E slot, tried another PSU (Silverstone 600watt), tried another processor, Q9450, removed one stick of memory. Every variation gives the same result: doesn't post, endless start-shutdown cycle. Second system: Asus A8N-SLI Deluxe, Athlon 64 3500, Corsair HX620 PSU, 4x1gb of Corsair PC3200 XL 2-2-2-5 memory, Radeon 1900XT. Also no overclocking or BIOS mods of the CPU, memory or video card. This system also worked perfectly for an hour before I attempted to install the 4870. After installation of the 4870, same sputtering start of the 4870's fan and no post. Reinstalled the 1900XT and the fan on the 1900XT goes to high but unlike a regular boot, stays at high, it never spins down. The system, of course, also never posts or boots. Unlike the Maximus Formula, the board doesn't shutdown and restart automatically. It stays powered on but never posts. No hard drive activity in both systems. Any idea what's going on? The only two common components between these two systems are the 4870 and the Corsair PSU. The Corsair is approved by ATI to operate a single 4870 and Corsair says it's capable of running two 4870's. The PSU has also operated flawless in the first system for six months and it operated perfectly for the hour I had the second system running with the 1900XT before I tried to install the 4870. I think the culprit in the 4870 but how could a 4870 screw up a motherboard so badly that it no longer functions even with an older card? Anyone seen or heard of similar experiences?